Alright, so here is the situation my girlfriend and I are in. One of our two RES turtles has been exhibiting some strange behavior recently (Scratching at the basking platform with back legs, excessive basking, change in diet, etc.) Upon further research we discovered that these were all signs of potentially being gavid. We're not exactly sure the sex of either turtle but they are both roughly the same size, claw length is almost identical, and carapace is smooth underneath for both of them so we are assuming they are both female.

We took the turtle we assume to be gavid and put her in a little nesting area we built but she hasn't laid any eggs. Because of how quickly this situation arose we don't have an additional heat/UV lamp for the nesting area yet so we let her stay in the nesting area for 2 hours and then put her back in the tank. Upon return to the tank, our other turtle was becoming unusually aggressive towards her (Biting at her back legs and neck) which scared us. We were forced to separate them which has been a huge ordeal.

My questions are

A) How can we be sure that both turtles are the same sex? We don't have the space for a second tank and are hoping they are both females and just freaked over all the changes accompanying the situation.

B) If our turtle is indeed gavid, at what point should she be laying eggs and what signs should we be on the look out for that point towards her being sick?

This all happened so suddenly and we are both a little irked at the lack of information presented by the pet store when we initially got them 3 years ago. I've been reading up everything I can but I'm no expert and just trying to get some confirmation and advice for these poor little guys.

If posting pictures of them will help with determining the sex or any other info is needed please let me know. Thank you for any and all advice!